13,738 research outputs found
Nanocrystalline semiconductors: synthesis, properties, and perspectives
The preparation of hollow particles of ZnO by calcination of hydrozincite coated poly(styrene)
beads is reported. Synthetic studies have been performed on such polymer/inorganic composite
precursors in order to establish the optimum conditions for the preparation of the ZnO particles. The
morphological properties of the powders were characterised by optical microscopy and scanning
electron microscopy. The micrometric ZnO particles show morphological characteristics related to the
template used in their preparation
Nanostructured semiconductor materials for dye-sensitized solar cells
Since O'Regan and Grätzel's first report in 1991, dye-sensitized solar cells (DSSCs) appeared immediately as a promising low-cost photovoltaic technology. In fact, though being far less efficient than conventional silicon-based photovoltaics (being the maximum, lab scale prototype reported efficiency around 13%), the simple design of the device and the absence of the strict and expensive manufacturing processes needed for conventional photovoltaics make them attractive in small-power applications especially in low-light conditions, where they outperform their silicon counterparts. Nanomaterials are at the very heart of DSSC, as the success of its design is due to the use of nanostructures at both the anode and the cathode. In this review, we present the state of the art for both n-type and p-type semiconductors used in the photoelectrodes of DSSCs, showing the evolution of the materials during the 25 years of history of this kind of devices. In the case of p-type semiconductors, also some other energy conversion applications are touched upon. © 2017 Carmen Cavallo et al
Synthesis of titanate nanofibers co-sensitized with ZnS and Bi2S3 nanocrystallites and their application on pollutants removal
The synthesis of nanocomposite materials combining titanate nanofibers (TNF)
with nanocrystalline ZnS and Bi2S3 semiconductors is described in this work.
The TNF were produced via hydrothermal synthesis and sensitized with the
semiconductor nanoparticles, through a single-source precursor decomposition
method. ZnS and Bi2S3 nanoparticles were successfully grown onto the TNF's
surface and Bi2S3-ZnS/TNF nanocomposite materials with different layouts were
obtained using either a layer-by-layer or a co-sensitization approach. The
samples' photocatalytic performance was first evaluated through the production
of the hydroxyl radical using terephthalic acid as probe molecule. All the
tested samples show photocatalytic ability for the production of this oxidizing
species. Afterwards, the samples were investigated for the removal of methylene
blue. The nanocomposite materials with best adsorption ability for the organic
dye were the ZnS/TNF and Bi2S3ZnS/TNF. The removal of the methylene blue was
systematically studied, and the most promising results were obtained
considering a sequential combination of an adsorption-photocatalytic
degradation process using the Bi2S3ZnS/TNF powder as a highly adsorbent and
photocatalyst material.Comment: 26 pages, 10 figure
Dimerization and low-dimensional magnetism in nanocrystalline TiO2 semiconductors doped by Fe and Co
The report is devoted to an analysis of the structural and magnetic state of the nanocrystalline diluted magnetic semiconductors based on TiO2 doped with Fe and Co atoms. Structural and magnetic characterization of samples was carried out using X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR) spectroscopy, SQUID magnetometry, and the density functional theory (DFT) calculations. Analysis of the experimental data suggests the presence of non-interacting paramagnetic Fe3+ and Co2+ ions in the high-spin state and negative exchange interactions between them. The important conclusions is that the distribution of dopants in the TiO2 matrix, even at low concentrations of 3d-metal dopant (less than one percent), is not random, but the 3d ions localization and dimerization is observed both on the surface and in the nanoparticles core. Thus, in the paper the quantum mechanical model for describing the magnetic properties of TiO2:(Fe, Co) was suggested. The model operates only with two parameters: paramagnetic contribution of non-interacting 3d-ions and dimers having different exchange interactions between 3d magnetic carriers. © Published under licence by IOP Publishing Ltd
Bulk Nanocrystalline Thermoelectrics Based on Bi-Sb-Te Solid Solution
A nanopowder from p-Bi-Sb-Te with particles ~ 10 nm were fabricated by the
ball milling using different technological modes. Cold and hot pressing at
different conditions and also SPS process were used for consolidation of the
powder into a bulk nanostructure and nanocomposites. The main factors allowing
slowing-down of the growth of nanograins as a result of recrystallization are
the reduction of the temperature and of the duration of the pressing, the
increase of the pressure, as well as addition of small value additives (like
MoS2, thermally expanded graphite or fullerenes). It was reached the
thermoelectric figure of merit ZT=1.22 (at 360 K) in the bulk nanostructure
Bi0,4Sb1,6Te3 fabricated by SPS method. Some mechanisms of the improvement of
the thermoelectric efficiency in bulk nanocrystalline semiconductors based on
BixSb2-xTe3 are studied theoretically. The reduction of nanograin size can lead
to improvement of the thermoelectric figure of merit. The theoretical
dependence of the electric and heat conductivities and the thermoelectric power
as the function of nanograins size in BixSb2-xTe3 bulk nanostructure are quite
accurately correlates with the experimental data.Comment: 35 pages, 24 figures, 4 tables, 52 reference
Synthesis of Colloidal Mn2+:ZnO Quantum Dots and High-TC Ferromagnetic Nanocrystalline Thin Films
We report the synthesis of colloidal Mn2+-doped ZnO (Mn2+:ZnO) quantum dots
and the preparation of room-temperature ferromagnetic nanocrystalline thin
films. Mn2+:ZnO nanocrystals were prepared by a hydrolysis and condensation
reaction in DMSO under atmospheric conditions. Synthesis was monitored by
electronic absorption and electron paramagnetic resonance (EPR) spectroscopies.
Zn(OAc)2 was found to strongly inhibit oxidation of Mn2+ by O2, allowing the
synthesis of Mn2+:ZnO to be performed aerobically. Mn2+ ions were removed from
the surfaces of as-prepared nanocrystals using dodecylamine to yield
high-quality internally doped Mn2+:ZnO colloids of nearly spherical shape and
uniform diameter (6.1 +/- 0.7 nm). Simulations of the highly resolved X- and
Q-band nanocrystal EPR spectra, combined with quantitative analysis of magnetic
susceptibilities, confirmed that the manganese is substitutionally incorporated
into the ZnO nanocrystals as Mn2+ with very homogeneous speciation, differing
from bulk Mn2+:ZnO only in the magnitude of D-strain. Robust ferromagnetism was
observed in spin-coated thin films of the nanocrystals, with 300 K saturation
moments as large as 1.35 Bohr magneton/Mn2+ and TC > 350 K. A distinct
ferromagnetic resonance signal was observed in the EPR spectra of the
ferromagnetic films. The occurrence of ferromagnetism in Mn2+:ZnO and its
dependence on synthetic variables are discussed in the context of these and
previous theoretical and experimental results.Comment: To be published in the Journal of the American Chemical Society Web
on July 14, 2004 (http://dx.doi.org/10.1021/ja048427j
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